Experiments with Shifting Gears and Turn Radius

[Jaybird180]

This past weekend I took my children out riding to our practice field. As "luck" would have it, only 1 of the 3 bikes wanted to play so my daughter after doing the first set of exercises I had for her allowed her little brother ride her CRF110. He had to get on his tip-toes but he was fine once he got it under power.

Later the day, I was able to get his CRF50 started and I gave him some exercises to do on his bike. The last exercise I gave him for the day was a high speed run from one end of the football field around the goalposts and back around the other one. At a certain point, he began to get the idea of rolling on the gas through the turn! SUCCESS!!!

I decided to jump on my daughter's bike to try to follow him. About midfield he began to pull away ever so slightly. The race was on!

Because he was using only a single gear (3rd I think), I was able to get the bike slowed, downshifted, turned around the pole and back into the power in a lower gear before he was able to get his bike pointed toward the next goalpost with his VERY WIDE turns. I tried the experiment several times in various gears and I noticed the marked willingness of the bike to whip around the pole at small radiuses the lower the gearing. I also noticed that I was able to hold more throttle under control with a tight turn the lower the gear as well.

Most of the time, he was able to hold enough cornerspeed that he was able to beat me back to 1/4 field and then he'd pull away very slightly again. It wasn't as lopsided a race as one would think. Many times we were side-by-side and hard on the gas. That was fun!

At any rate...I'm wondering if there's a corollary on streetbikes with turn radius and gearing. Although I can't imagine needing to whip a streebike around a pole is there a practical way where I can experiment with this idea? I'm wondering if turn radius isn't only speed and bar pressure but there may be a gearing component as well.

Next question: I'm looking for suggestions on teaching a 5-yo how to shift gears.

[Hotfoot]

Higher RPM in a corner does make a difference in motorcycle handling.

Take a look at this article:

https://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=2182

There is also the effect of greater engine braking approaching the turn, which may have allowed you to shorten your braking distance, or use less brake and get a more accurate entry speed. 

[Hotfoot]

What do you mean by "hold more throttle under control"? 

[Jaybird180]

1 hour ago, Hotfoot said:

What do you mean by "hold more throttle under control"? 

Meaning I was able to use the power to to help the bike turn and then shoot out instead of killing the RPM. RPM also helped keep the wheels underneath me as I was riding much more loose than I ever have been able to on anything bigger. 

I'll get right on the article you posted.

[Jaybird180]

1 hour ago, Hotfoot said:

Higher RPM in a corner does make a difference in motorcycle handling.

Take a look at this article:

https://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=2182

There is also the effect of greater engine braking approaching the turn, which may have allowed you to shorten your braking distance, or use less brake and get a more accurate entry speed. 

Okay, I got it that the engine contributes to stability if the crankshaft rotates in the same plane of motion as the wheels. In my description above, I noticed less willingness of the bike to turn in the higher gears and I think I was feeling this added stability at very slow speeds in the vector transitions; I was probably 1-3 feet from the pole when turned 180* and most times, I could probably stick out my arm, flip the bike around and then touch the pole going the other way...getting a bit loose during those times.

Now, to make a turn, stability is our enemy. We need just enough to keep the bike at the desired lean angle, but no more than that as it becomes an obstacle to getting the nose pointed in the desired direction. I hypothesize that it would seem that there's less rotating mass at higher gear (lower RPM), then we should be able to change direction faster. This didn't agree with the results I got on the CRF110 which is a single cylinder bike. I'd also have to work the math on the gearing to know which would have lower rotating mass assuming the same rear wheel speeds as you have larger cogs (more mass) to contend with inside the transmission...except my understanding is that on motorcycle transmissions, all the gears are rotating at all times - I'll have to confirm this.

Yes, I did exploit engine braking. Going down to 1st got the rear wheel hopping and it was more effective than the brakes.

[Hotfoot]

12 hours ago, Jaybird180 said:

Meaning I was able to use the power to to help the bike turn and then shoot out instead of killing the RPM. RPM also helped keep the wheels underneath me as I was riding much more loose than I ever have been able to on anything bigger. 

I'll get right on the article you posted.

So was the rear wheel spinning up more? 

[Jaybird180]

I would have to say yes* it was spinning more because I found that with power on in the lower gears I didn't have the widening of the turn the same way as in higher gears- I had better control over momentum; I could more quickly change speed, turn and shoot out.

Caveat to yes is that with very little experience with spinning tires and on the grass surface, I have a little bit of haze on determining the relative spinning in the two conditions and have to depend on my ability to revisit the experience to put it into relatable words.

[Hotfoot]

13 hours ago, Jaybird180 said:

Okay, I got it that the engine contributes to stability if the crankshaft rotates in the same plane of motion as the wheels. In my description above, I noticed less willingness of the bike to turn in the higher gears and I think I was feeling this added stability at very slow speeds in the vector transitions; I was probably 1-3 feet from the pole when turned 180* and most times, I could probably stick out my arm, flip the bike around and then touch the pole going the other way...getting a bit loose during those times.

Now, to make a turn, stability is our enemy. We need just enough to keep the bike at the desired lean angle, but no more than that as it becomes an obstacle to getting the nose pointed in the desired direction. I hypothesize that it would seem that there's less rotating mass at higher gear (lower RPM), then we should be able to change direction faster. This didn't agree with the results I got on the CRF110 which is a single cylinder bike. I'd also have to work the math on the gearing to know which would have lower rotating mass assuming the same rear wheel speeds as you have larger cogs (more mass) to contend with inside the transmission...except my understanding is that on motorcycle transmissions, all the gears are rotating at all times - I'll have to confirm this.

Yes, I did exploit engine braking. Going down to 1st got the rear wheel hopping and it was more effective than the brakes.

I don't agree that stability is our enemy. Yes the added stability would make the bike harder to steer initially, but a CRF110 is never going to be difficult to get to turn. However, more stability leaned over could make that particular bike easier to manage in a very tight turn, less twitchy and not as reactive to the rider moving around or oversteering, etc., which seems to me to be a bigger consideration on a little dirt bike than getting it to turn in the first place.

[Jaybird180]

This is the context in which I used the word Stability

Stability
sta-bil-i-ty  [stuh-bil-i-tee]   

noun, plural stabilities. 

1. the state or quality of being stable.

2. firmness in position.

3. continuance without change; permanence.

4. Chemistry. resistance or the degree of resistance to chemical change or disintegration.

5. resistance to change, especially sudden change or deterioration:
(The stability of the economy encourages investment.)

6. steadfastness; constancy, as of character or purpose:
(The job calls for a great deal of emotional stability.)

7. Aeronautics. the ability of an aircraft to return to its original flying position when abruptly displaced.

 

Source: Dictionary.com

[Jaybird180]

34 minutes ago, Hotfoot said:

I don't agree that stability is our enemy. Yes the added stability would make the bike harder to steer initially, but a CRF110 is never going to be difficult to get to turn. However, more stability leaned over could make that particular bike easier to manage in a very tight turn, less twitchy and not as reactive to the rider moving around or oversteering, etc., which seems to me to be a bigger consideration on a little dirt bike than getting it to turn in the first place.

There are some proponents of the idea of having a little bit of gas on at the steering input. I think it's possible that riding "little" (relative to the rider) dirtbikes could be a case for that as a technique. Certainly it's easier to manage rear wheel traction in a lower gear when using this technique.

On a road bike I'm hard pressed to think of how using a lower gear could be exploited. We are often more concerned with getting corner exit drive then making a tight turn...only case coming to mind where it could be useful would be Turn2 at NCBike. It's a right handed DR and nearly blends into T1 as if it's a double apex with the DR at the end, then there's a short chute downhill to T3 which is a left. One could intentionally backshift to get the extra maneuverability for T2, accept the penalty of being at the top of the rev range at the T2 exit and immediately upshift to the next gear prior to T3 entry point.

[Hotfoot]

Just so we are clear, I'm talking about higher rpm while already leaned over, which is not the same thing as having some throttle on while steering the bike. The bike feels more stable in the turn at higher rpm because the lean angle is set and it doesn't want to change because of the increased gyroscopic effect. 

For me on the S1000rr it can feel more stable at a higher rpm (lower gear) in a slow tight  turn like the last few turns at Streets of Willow or Turn 9 at ACS, less reactive to rider movement or rough throttle inputs because the lean angle doesn't change as easily, and the more immediate throttle response when picking up the gas helps me to get better throttle control. 

Feeling a desire or need to have some throttle on when ENTERING a turn tells you something about your entry speed, do you remember what? 

[Jaybird180]

46 minutes ago, Hotfoot said:

 

Feeling a desire or need to have some throttle on when ENTERING a turn tells you something about your entry speed, do you remember what? 

Probably that your entry speed is too low. I may have given the wrong impression and I thank you for pulling on me. I do recall shutting off the gas on entry and at a point during the turn getting back into the gas. I confess to being greedy with it however even though I was trying to teach my children to be smooth with it...I was trying to catch my son and the power-weight ratio didn't help much, but this experience forced me to stalk him for several "laps" up/down the field until I could make a safe pass up the inside, knowing  he'd go wide.

[EDIT: on further thought, I may have to look it up to know what it means to feel a need to use throttle on entry. Any hints on where to look?]

 

46 minutes ago, Hotfoot said:

Just so we are clear, I'm talking about higher rpm while already leaned over, which is not the same thing as having some throttle on while steering the bike. The bike feels more stable in the turn at higher rpm because the lean angle is set and it doesn't want to change because of the increased gyroscopic effect. 

 

Not sure if I understand what you perceive as a communication lag.

 

46 minutes ago, Hotfoot said:

For me on the S1000rr it can feel more stable at a higher rpm (lower gear) in a slow tight  turn like the last few turns at Streets of Willow or Turn 9 at ACS, less reactive to rider movement or rough throttle inputs because the lean angle doesn't change as easily, and the more immediate throttle response when picking up the gas helps me to get better throttle control. 

This confirms my suspicion.

[Lnewqban]

There is more force applied onto the rear contact patch when the transmission is working in lower gears.

On surfaces of poor traction (grass, dirt, etc.), the rear tire has more authority (breaks loose and pushes the bike around easier) when first or second gears are engaged.

[Jaybird180]

1 hour ago, Lnewqban said:

There is more force applied onto the rear contact patch when the transmission is working in lower gears.

On surfaces of poor traction (grass, dirt, etc.), the rear tire has more authority (breaks loose and pushes the bike around easier) when first or second gears are engaged.

Why is that?

[Hotfoot]

4 hours ago, Jaybird180 said:

Not sure if I understand what you perceive as a communication lag.

Huh? Did I say something about a communication lag...? 

[Lnewqban]

4 hours ago, Jaybird180 said:

Why is that?

Because all the gears and sprockets that link the crankshaft with the rear wheel act like a lever: the rotational speed of the rear wheel gets reduced while its applicable torque increases.

For the same degree of openning of the throtle, resisting load and rpm's, the engine generates certain amount of torque or rotational force.

We have to work around that more or less constant amount of torque, playing with the gears, just like it happens with a bicycle.

For a greater resistive load (going uphill, for example), we have to sacrifice rotational speed of the rear wheel in order to have greater torque there; hence, we switch to lower gears.

One trick for riding in the rain is to corner using a taller than normal gear, which "weakens" the available torque of the rear wheel, which creates an extra safety margin regarding any mistake with excessive throttle that could overwhelm the marginal available traction.

https://www.youtube.com/watch?v=3Tc3VIDQvh0

[Jaybird180]

Wouldn’t the changes in leverage be experienced at the power plant end of the system? If traveling at any given speed in the 1st gear does the road, tire, wheel, sprocket, chain or countershaft know the difference between doing the same speed in 4th gear? I haven’t seen enough to be convinced that those forces are different, save for the power pulses (maybe); the same amount of WORK is being performed despite the advantages of leverage.

 

[Lnewqban]

7 hours ago, Jaybird180 said:

Wouldn’t the changes in leverage be experienced at the power plant end of the system?

Absolutely!

That is the whole reason for the need of selective gears: to keep the engine rotating within the range of rpm's that produces usable torque (and work) for a wider range of rpm's of the rear wheel (which translates into forward speed of the motorcycle).

Except during the brief periods of coasting and engine breaking, the work of the engine pulls the motorcycle forward against the resisting forces of inertia (during acceleration) aerodynamic drag (at relatively high speeds) and (when climbing a hill) gravity.

The only thing that dramatically changes the torque (and work) that the engine can deliver is the "twist of the throttle": more entering fuel and air means more powerful internal combustion, which means more internal heat and delivered torque (and work).  That is true for certain range of engine's rpm and until we reach the point of full open throttle (maximum intensity of combustion and delivered torque), which is what dyno charts show.

The work developed by the rear tire is always the product of its rotational speed (rpm's) times the torque it is able to deliver, which is exactly the same value as the product of its linear speed (forward speed of the bike) times the rearward force exerted over the pavement.  The value of the work developed by the engine is always a little higher than the previous one, as some energy (in the form of transferred forces down the gears and chain and sprockets) is lost in the links between the crankshaft and rear tire.

When the bike is moving at sustained 60 mph on a horizontal road, the position of the throttle is fixed, allowing intake of the exact amount of fuel and air that keeps two forces in balance: pushing forward force and resisting rearward force.  If the bike starts climbing a hill and the throttle remains fixed (work delivered by the engine remains the same), the force resisting the rotation of the rear wheel increases due to the addition of the gravity effect.  As no additional work from the engine is available, the other factor of the formula (torque X rpm) must decrease, resulting in a new state of balance at lower rpm's.  

The natural reaction to that is the slowing down of the rotational speed of the rear tire and forward speed of the motorcycle and reduction in rpm's of the engine.  We can only allow certain amout of that reduction of the rpm's of the engine before the engine becomes real weak.  If we wish keeping the same on-flat-road during the climb, we need to open the thottle up (more work delivered by the engine translates into resuming speed).  If the steepness of the hill is excessive to achieve a new state of balance, even at full open throttle (no additional available work), we need to sacrifice bike speed in order to increase force on the rear contact patch via dowshifting. 

Returning to your original question:  When the bike is moving at sustained speed on a horizontal road, the two forces are in balance: pushing forward force and resisting rearward force. If you open the throttle up some (more delivered work), the bike will accelerate due to additional torque reaching the rear tire, until reaching a new rpm X torque balance. If you open the throttle up a lot, the bike will do a wheelie due to excessive acceleration and abundant traction.  If traction is not that abundant, then the additional available work must go to break the grip between the contact patch and the surface, spinning the rear wheel.

[Jaybird180]

20 hours ago, Hotfoot said:

Huh? Did I say something about a communication lag...? 

I perceived that you felt a need to clarify for my sake- that I missed something in translation. Did I misunderstand that you thought I misunderstood? (LoL)

[Jaybird180]

4 hours ago, Lnewqban said:

Absolutely!

That is the whole reason for the need of selective gears: to keep the engine rotating within the range of rpm's that produces usable torque (and work) for a wider range of rpm's of the rear wheel (which translates into forward speed of the motorcycle).

Except during the brief periods of coasting and engine breaking, the work of the engine pulls the motorcycle forward against the resisting forces of inertia (during acceleration) aerodynamic drag (at relatively high speeds) and (when climbing a hill) gravity.

The only thing that dramatically changes the torque (and work) that the engine can deliver is the "twist of the throttle": more entering fuel and air means more powerful internal combustion, which means more internal heat and delivered torque (and work).  That is true for certain range of engine's rpm and until we reach the point of full open throttle (maximum intensity of combustion and delivered torque), which is what dyno charts show.

The work developed by the rear tire is always the product of its rotational speed (rpm's) times the torque it is able to deliver, which is exactly the same value as the product of its linear speed (forward speed of the bike) times the rearward force exerted over the pavement.  The value of the work developed by the engine is always a little higher than the previous one, as some energy (in the form of transferred forces down the gears and chain and sprockets) is lost in the links between the crankshaft and rear tire.

When the bike is moving at sustained 60 mph on a horizontal road, the position of the throttle is fixed, allowing intake of the exact amount of fuel and air that keeps two forces in balance: pushing forward force and resisting rearward force.  If the bike starts climbing a hill and the throttle remains fixed (work delivered by the engine remains the same), the force resisting the rotation of the rear wheel increases due to the addition of the gravity effect.  As no additional work from the engine is available, the other factor of the formula (torque X rpm) must decrease, resulting in a new state of balance at lower rpm's.  

The natural reaction to that is the slowing down of the rotational speed of the rear tire and forward speed of the motorcycle and reduction in rpm's of the engine.  We can only allow certain amout of that reduction of the rpm's of the engine before the engine becomes real weak.  If we wish keeping the same on-flat-road during the climb, we need to open the thottle up (more work delivered by the engine translates into resuming speed).  If the steepness of the hill is excessive to achieve a new state of balance, even at full open throttle (no additional available work), we need to sacrifice bike speed in order to increase force on the rear contact patch via dowshifting. 

Returning to your original question:  When the bike is moving at sustained speed on a horizontal road, the two forces are in balance: pushing forward force and resisting rearward force. If you open the throttle up some (more delivered work), the bike will accelerate due to additional torque reaching the rear tire, until reaching a new rpm X torque balance. If you open the throttle up a lot, the bike will do a wheelie due to excessive acceleration and abundant traction.  If traction is not that abundant, then the additional available work must go to break the grip between the contact patch and the surface, spinning the rear wheel.

Thank you. No problems here.

[Jaybird180]

On 4/20/2018 at 4:27 PM, Lnewqban said:

On surfaces of poor traction (grass, dirt, etc.), the rear tire has more authority (breaks loose and pushes the bike around easier) when first or second gears are engaged.

Perhaps we should have been discussing this instead.

Only corollary that I could think of would be Garry McCoy’s sliding style of cornering, where he’d light up the rear, swinging the thing around the steering head. Caught a lot of flak until he won a GP race like that AND it was found that the tire was no worse for wear as only the top surface was heating up.

[Lnewqban]

20 hours ago, Jaybird180 said:

Perhaps we should have been discussing this instead.

Only corollary that I could think of would be Garry McCoy’s sliding style of cornering, where he’d light up the rear, swinging the thing around the steering head. Caught a lot of flak until he won a GP race like that AND it was found that the tire was no worse for wear as only the top surface was heating up.

 

 

 

https://motomatters.com/interview/2012/04/12/casey_stoner_explains_how_to_slide_a_mot.html

 

Casey Stoner Explains How To Slide a MotoGP Bike:

"It's something that only works in certain corners in this type of racing, it doesn't work in all the corners. When it does work, sometimes it can be a bit scary; you can go into the corner, and if you make a small mistake when you are sliding, the finish of it can be a catastrophe. When your heart beats really hard is when you slide when you don't really want to,".......

 "There's different techniques to different corners and when they should be used, depending on grip levels, and a lot of different things. Unfortunately, most of the time these days, sliding is not the fastest way, there's only some corners where it can still work."

 

About teaching a 5-year child how to shift gears, I recommend you this reading:

https://books.google.com/books/about/Casey_Stoner_Pushing_the_Limits.html?id=npA1AgAAQBAJ

[Jaybird180]

Clicked on the Stoner book and tried to find it in print version. Not available until Nov 2018!!!!

[Jaybird180]

On 4/24/2018 at 7:10 PM, Jaybird180 said:

Clicked on the Stoner book and tried to find it in print version. Not available until Nov 2018!!!!

Finally was able to order a paperback